The invention relates generally to a spinal implant instrument for use in intervertebral spinal fusions, and more specifically, to an improved method of protection for neural elements during intervertebral disc space distraction, disc space reaming and tapping, and placement of intervertebral disc space bone grafts and prosthetic devices.
The spinal column is formed from a number of vertebrae, which in their normal state, are separated from each other by cartilaginous intervertebral discs. These discs form a cushion between adjacent vertebrae, resisting compression along the support axis of the spinal column, but permitting limited movement between the vertebrae to provide the characteristic flexible movement of the healthy spine. Injury, disease, or other degenerative disorders may cause one or more of the intervertebral discs to shrink, collapse, deteriorate, or become displaced, herniated, or otherwise damaged.
Intervertebral stabilization by fusion of adjacent vertebrae has proven successful in permanently preserving intervertebral spacing. However, a number of technical barriers exist, including, for example, the retraction of neural elements out of the normal anatomic position, to a temporarily disadvantageous position, to allow reaming, tapping, and insertion of various intervertebral disc space bone grafts and prostheses. The displacement of neural elements (nerve roots) in such fashion is not uncommonly followed by temporary, or even permanent injury to the nerve roots. This can present an unpleasant, nearly intolerable burning pain in the extremities. Also, traumatic openings in the nerve covering may occur, allowing the escape of cerebral spinal fluid, and requiring with subsequent repair, resulting scar and nerve restriction. There may also be disruption of motor and sensory nerve elements, potentially causing permanent numbness and weakness in the extremities, bladder, bowel, or genitalia.
Attempts to minimize the disadvantageous effects of retraction of neural elements include various nerve root retractors, designed to facilitate placement of the insertion tools against the adjacent nerves, and are commercially available. One disadvantage of these hand held retractors is instability. This instability may be caused by movement of the retractors by the insertion tools or by the shifting attention of the surgical assistant responsible for holding the retractors. Also, the physical bulk of the retractors themselves requires additional space in the limited confines of the intervertebral disc space being prepared for the intervertebral body prosthesis. In view of this, a need exists for a spinal implant insertion instrument to eliminate the need for separate nerve root retractors, and to protect neural elements from injury by the sequence of insertion tools as outlined above.
A need further exists for such a device designed for easy insertion, combining protection and nerve root retraction, at the same time speeding up the entire operative procedure in a safe and efficient manner.
Still another need exists for a method of distraction of the intervertebral disc space prior to insertion of the improved spinal implant. It is to that provision, for a device and method meeting these and other needs, that the present invention is primarily directed.
The subject invention provides a means for the protection of the nerve root during the insertion of a spinal implant on bone graft into an intervertebral disc space. Briefly described, in a preferred form, the present invention comprises a spinal implant insertion instrument, generally comprising a hollow body with an outer surface and an open interior surface. A fixed conically shaped curved guide with straight concave or convex contours extends from the bottom end of the hollow body. Additionally, a handle element, with a retractable conically shaped curved guide, is pivotally attached to the bottom end of the hollow body with an adjustable articulating hinge. The handle element is attached to the hollow body such that the retractable curved guide is positioned on an opposite side of the hollow body as the fixed curved guide. The cross-sectional area of the hollow body can be rectangular, elliptical or other shape, so long as it is of sufficient size to allow passage of instruments for reaming, tapping, and placement of intervertebral bone grafts or prosthetic devices.
In an alternative form, stringer elements are affixed to the outer surface of the fixed curved guides, where the stringer elements traverse the lengths of the curved guides. The stringer elements add additional strength to the curved guides.
In a preferred form, the spinal instrument comprises a primary locking mechanism. The primary locking mechanism locks the curved guides in the fully extended position by securing the handle element to the hollow body. Preferably, the locking mechanism is a spring-loaded retraction ring, which locks and secures the handle element by engaging a locking tab, which extends from the handle proximal end.
The spinal implant insertion instrument can be fabricated from biocompatible materials including, without limitation, titanium, surgical alloys, stainless steel, or any other material suitable for fabrication of surgical instruments.
In a preferred method use, the curved guides are positioned between a first vertebra and a second vertebra, with the curved guides being in the un-retracted position. The outer surface of the fixed curved guide is positioned against the lumbar dural tube. The hinged joint allows simultaneous retraction of the nerve root by compressing the handle element into the hollow body. The simultaneous retraction of the nerve root away from the lumbar dural tube allows for a safe retraction of the neural elements, eliminating the need for an independent retraction means, which would add additional bulk in a confined space, which in the present art, contributes to inappropriate compression of neural elements. In the retracted position, the internal diameter of the hollow body is sufficient to allow passage of instruments for reaming, tapping, and placement of intervertebral bone grafts or prosthetic devices.
These and other objects, features and advantages of the present invention will be more readily understood, with reference to the detailed description below, read in conjunction with the accompanying drawings.